Various research has been conducted with respect to the optimization of designs for distillation and fractionation columns or zones, i.e., a contacting column or zone wherein liquid and vapor phases are counter currently contacted to effect separation of a fluid mixture, as for example, by contacting of the vapor and liquid phases on a series of vertically spaced horizontal trays or plates mounted within the column. The design research has primarily focused on the design of different tray structures to improve the efficiency of the overall separation process. Attempts have also been made to design superior packing materials to be placed within the column to enhance the separation process.
The distillation process as traditionally known in the art is a method for separating the individual components of a mixture by utilizing the differences in their vapor pressure. In particular, in the chemical industry, a variety of tray designs have been developed to increase the efficiency of the mass transfer. Improvements in the design of distillation columns led to the use of different types of packing for filling the insides of such distillation columns. For instance, the packing now in use includes wire mesh packing, sheet metal packing, ceramic packing, glass packing, and synthetic resin packing. Many types of packing have been developed for use in distillation and fractionation columns. In general, these packing materials facilitate contact between the liquid and vapor streams by causing more uniform distribution of liquid and vapor over the surface of the packing. Early forms of structured packing include Stedmen packing, described in U.S. Pat. No. 2,047,444. In general, structured packing refers to packing where individual members have a specific orientation relative to each other and to the axis of the column or tower. Random packing, such as the use of Raschig saddles, is also used in the industry.
One type of packing that is widely used consists of a plurality of corrugated plates that contact each other and are disposed in parallel relationship to the column axis. Corrugated plates of this type can be constructed of different types of material such as sheet metal and woven wire fabric. When the corrugated plates are made of sheet metal, uniform distribution of the liquid over the plates is impeded because the liquid tends to channel along the fold troughs. To improve liquid distribution over the corrugated plates, it is known to use apertures in the plates so that a portion of the liquid flowing along one side of the plate is deflected to the opposite side of the plate as it encounters an aperture. An example of such a plate is described in U.S. Pat. No. 4,296,050 to Meier. A column packing made with corrugations and textured surfaces for improved performance especially under turn down conditions is disclosed in U.S. Pat. No. 5,132,056 to Lockett et al. An improved corrugated plate design to achieve a higher density of plates within a given cross-sectional area of the column to achieve enhanced mass and/or heat transfer between the liquid and vapor streams flowing within the column is set forth in U.S. Pat. No. 5,413,741.
Other types of packing besides the corrugated and textured surface plates include packing that consist of individual packing elements. The efficiency in using such packing elements is generally considered to be increased by providing the elements in a random order such as taught in U.S. Pat. No. 4,376,081 to Leva which discloses an element that has a base that has a surface contour which is generated by the rotation of a two-dimensional curve having reverse curvature through an approximate angle range of from 10 to 180 around a straight line that lies within the plane of the curve. The base of the packing element is further provided with slots and depending tongues. A distillation column packing in the form of a spherical body constructed by assembling a pair of hemispherical members of the same shape and structure wherein each of the hemispherical members includes a suitable number of cutout openings formed on the surface portion thereof is shown in U.S. Pat. No. 4,159,817 to Ikawa.
The concept of co-current contact with the liquid and vapor streams within the overall counter-current flow of these two streams within the column has been suggested to enhance the overall capacity of the separation. One example of this concept is the tray design set forth in U.S. Pat. No. 4,361,469 to Trutna. The column has a plurality of vertically spaced trays each consisting of two vertically spaced rows of strips that are parallel and where the strips of the lower row are centered below the spaces of the upper row, and has a separator above each of the trays consisting of plural vertically spaced rows of upwardly facing channels that are parallel and of which the channels of one row are centered between the channels of the adjacent row or rows, the trays and separators occupying a major portion of the cross sectional area of the tower and the remainder of the cross sectional area of the tower being occupied by liquid downcomers.
Improvements in distillation and fractionation column design are needed to increase the efficiency or capacity of the overall separation process and thereby reduce operating and/or fixed costs. Improved designs preferably would take advantage of the entire volume within the column for use in the separation process and utilize efficient contacting of the phases followed by efficient separation of same.